Attorneys for Oskar Groening, 96, filed the appeal with prosecutors in Lueneburg, where he was convicted in 2015 as an accessory to the murder of 300,000 Jews. He was sentenced to four years in prison, but hasn't yet spent any time behind bars because of the appeals process.

According to Spiegel and other German media outlets, prosecutors' in the city of Lueneburg ruled against the clemency request on Wednesday after consultation with the panel of judges who convicted Groening.

A doctor had previously declared Groening fit to go to prison so long as there is appropriate medical care.

Groening exhausted his last chance at legal appeals in December when the country's highest court rejected his attorneys' argument that imprisoning him would violate his constitutional right to life and physical safety.

The Federal Constitutional Court noted, however, that German law allows for prison sentences to be interrupted if a prisoner's health deteriorates significantly.

Groening, who has been dubbed the "accountant of Auschwitz," testified at his trial that he oversaw the collection of prisoners' belongings and ensured that valuables and cash were separated to be sent to Berlin. He said he witnessed individual atrocities, but didn't acknowledge participating in any crimes.

The court that convicted him ruled, however, that he was part of the "machinery of death," helping the camp function and collecting money stolen from the victims to help the Nazi cause, and thus could be convicted as an accessory to the murders committed there.